XVI.   COLUMN FEET SURROUNDED BY AND FILLED WITH
DIRT AND MOISTURE

The condition of the average column-foot is simply deplorable. This is caused by failing to raise it so high above the street as to prevent dirt from piling around it, and by omitting to fill its boxed spaces with concrete. When rusting at a column-foot is once well started, it is almost impossible to stop it from eating up the metal rapidly.

XVII.  INSUFFICIENT BASES FOR PEDESTALS.

False ideas of economy on the part of projectors and indiference on the part of some unscrupulous contractors occasionally cause the use of pedestal bases altogether too small for the loads that come upon them, especially where the bearing capacity of the soil is low. The result is sunken pedestals and cracked metal-work. In figuring the pressure on the base of the pedestals, it is not sufficient to recognize only the direct live and dead loads, but it is necessary also to compute the additional unequal intensities of loading caused by both longitudinal and transverse thrusts.

Concerning the question of the extent to which the faults just outlined exist in the older elevated railroads of this country, the author would refer the reader to the résumé of discussions on his paper, and to the report of Mr. Hedrick which it contains.

About the most important object to attain in constructing an elevated railroad is to have a perfectly smooth and durable track; and no trouble or expense should be spared to secure it. For this reason the top flanges of the longitudinal girders, if the limiting heights of grade and clearance line permit, should be several inches higher than those of the cross-girders, the ties should all be planed to exact dimensions, tie-plates should be used over all ties, and the system of bolting of flooring to structure should be the most effective possible. The longitudinal girders should not be made continuous, or even semicontinuous over the cross-girders, but, when blocking up is necessary, short buckled plates should be placed over the

latter so as to provide a continuous surface for the ties.  Hook  bolts with  cold-pressed  threads  should  be  used  for  attaching